1. Field of the Invention
This invention relates to an etchant suitable for etching chalcogenide glass and oxychalcogenide glass, a method for etching chalcogenide glass and oxychalcogenide glass, and a glass optical member produced from this etching.
2. Description of Related Art
Generally, polishing and etching of a glass surface is commonly used to remove a metamorphic or deteriorated layer existing on the surface and foreign objects clinging to the surface. Removal of such a metamorphic layer or foreign objects by polishing, however, may leave latent scratches on the surface, and such latent scratches may unavoidably remain. If foreign objects cling to the glass surface or latent scratches remain on the glass surface, the glass greatly reduces the glass' mechanical strength.
Metal sulfide chalcogenide glasses, because of having high solubility of ionic substances, can be doped with a relatively large amount of light emitting substances. The metal sulfide chalcogenide glasses are, therefore, getting attentions as a material that may replace arsenic-sulfuric glass currently produced as chalcogenide glass fibers having a low solubility of ionic substances. The sulfuric chalcogenide glass, however, tends to have less stable crystallization than the arsenic-sulfuric glass, and the mechanical strength of the sulfuric chalcogenide glass may greatly suffer from foreign objects or latent scratches on the glass surface. When the sulfuric chalcogenide glass is made into a fiber by a drawing method, the glass surface may be crystallized around the foreign objects or latent scratches as nucleuses on the glass surface, and if crystallized once, the glass is hardly made into a fiber. Due to this ground, no example has been known in which the sulfuric chalcogenide glass is successfully made into a fiber by a drawing method, although the sulfuric chalcogenide glass can be doped with a relatively large amount of light emitting substances.
Foreign objects, latent scratches, etc. are generally removed by etching from the glass surface to make non-oxide glass having lesser stability of crystallization, e.g., fluoride glass. For example, U.S. Pat. No. 4,631,114 discloses removal of metamorphic layers, foreign objects, latent scratches on a preform or tube surface by etching with a special etchant over the preform or tube surface.
Necessary properties of the etchant are: first, the etchant will not increase micro undulation on the glass surface after removing the metamorphic layers, foreign objects, and latent scratches on the glass surface; second, the etchant will not promote latent scratches; and third, the etchant will not create any new metaphoric layer. When etching is made using an etchant dissatisfying those first to third conditions, the strength of the fiber may be deteriorated more than prior to the etching.
A chalcogenide glass, in particular, a sulfide glass, if inadvertently dipped in an etchant including an acid, generates poisonous hydrogen sulfide, etc., in accompanied with solution of the glass, and creates risks. Therefore, an etchant should be designed in the light of compositions of the glass as an etching target.
In sum, no etchant has been known so far which satisfies the first to third conditions above and which is designed in consideration of safeness as well.